Gravity, as a classical regulator for the Higgs field, and the origin of rest masses and electric charge

Abstract

The classical Einstein--Standard Model system with conformally invariant coupling of the Higgs field to gravity is investigated. We show that the energy-momentum tensor is not polynomial in the Higgs field, and hence it may have two singularities: In cosmological spacetimes the usual Big Bang type singularity with diverging matter field variables, and a second, less violent one (Small Bang), in which it is only the geometry that is singular but the matter field variables remain finite. In generic spacetimes, the latter provides a finite, universal upper bound for the pointwise norm of the Higgs field in terms of Newton's gravitational constant. We also show that, in the presence of Friedman--Robertson--Walker or Kantowski--Sachs symmetries, the energy density can have finite local minimum only if the transitivity hypersurfaces of the spacetime symmetries are locally hyperboloidal and their mean curvature is less than a finite critical value. In particular, in the very early era of an expanding universe or in a nearly spherically symmetric black hole near the central singularity, the Higgs sector does not have any instantaneous vacuum state, and hence its rest mass is not defined, and, via the Brout--Englert--Higgs (BEH) mechanism, the gauge and spinor fields do not get non-zero rest mass. For smaller mean curvature instantaneous symmetry breaking vacuum states of the Higgs sector emerge, yielding non-zero rest mass and electric charge for some of the gauge and spinor fields via the BEH mechanism. These rest masses are decreasing with decreasing mean curvature, but the charge remains constant. It is also shown that globally defined instantaneous vacuum states that are invariant with respect to the spacetime symmetries do not exist at all in the $k=1,0$ cosmological models and in Kantowski--Sachs spacetimes (e.g. inside spherically symmetric black holes).